Oren Nayar is perfect for rough, dirty, dusty, non-shiny surfaces - mud, soil, stucco walls, concrete, rubber etc. It's something you can see when you look at the moon - it doesn't look round, it looks almost flat, because of the rough surface. Oren Nayar is quite old though, I believe there are newer, better shading models available now. Still, it would be great to have anything that helps with these surfaces.